Terminal for contact or spark devices.



P. B. HEYL. TERMINAL FOR CONTACT 0R SPARK DEVICES. APPLICATION FILED MARfZO. 1915.

. PAUL B.. HEYL, OE NEW ROCHELLE, NEW YORK, ASSIGNOR TO COMMERCIAL RESEARCH COMPANY, 0E NEW YORK,

N. Y., A COEPOEATIONOF NEW YORK.

TERMINAL FOR, CONTACT OIR SPARK DEVICES.

Application led March 2o, 1915. Serial No. 15,983.

To all whom it may concern Be it known that I, PAUL It. HEYL, a citizen of the United States, residing at New Rochelle, county of Westchester, and State of New York, have invented certain new and useful Improvements in Terminals for 'Contact or Spark Devices, fully described and represented in the following specification and the accompanying drawings, forming a part of the same. l

This invention relates to improvements in terminals for contact or spark devices.

It has been the usual` practice heretofore to provide a contact device or spark point in electrical apparatus with a terminal facing or cap of platinum in order to insure that such facing or cap will remain clean and unaffected by electric sparks which may be formed between such terminal facings.

Platinum has beenl employed for such terminal facings particularly on account of its high melting point and its nonoxidizability or chemical inertness under various conditions of service, whereby it maintains a good metallic surface even though heated to a relatively high temperature by the sparks. Hardness sidered an advantage in a terminal facing for a contact device where the points are moved into and out of contact with each other. In fact it has sometimes been the practice to alloy a certain percentage of iridium with platinum in order to produce a terminal facingaf greater hardness. have found., however, that in practice it is difficult to make the contact Isurfaces fit exactly to each otherl throughout their entire extent, and therefore with very hard terminal facings any defect in accurate f1tting of the meetingsurfaces becomes a disadvantage, because the surfaces do not thereafter wear to a good contact with each other, or at least not for a long time.

I have found that a terminal facing for spark points or contact devices comprising a mixture of palladium and silver has important advantages over anything heretofore known to me. Palladium is a material having a high melting loyed with `silver the Amelting point of the alloy is very considerably reduced. rIhis apparently would be a great disadvantage and would seem to indicate that such an alloy would not be satisfactory for the pur- Specification o f Letters Patent.

has generally been conyductivity. Silver on point, but when al- Patented Dee. 2%., i915.

poses named. I have found, however, that as the thermal-conductivity of silver is very high, when mixed with palladium it gives to the alloy a thermal-conductivity considerably above that of palladium. Owing to this thermal-conductivity the heat generated by the spark is conducted away from the contact surface rapidly enough to insure that the surface portion will not reach a temperature above the melting point of the alloy. Where the current passing through the terminal facings does not have a great density, the terminal facings may be formed of an alloy composed principally of silver with a relatively small amount of palladium. In fact I have found that an alloy of silver with 2 per cent. of palladium will give satisfactory results under many circumstances.

When, however, the spark points or contact devices are to be exposed to an atmosphere containing sulfur compounds, the percentage of palladium should be increased. have found that an alloy of silver with 5 per cent. of palladium or more is substantially inert in any atmosphere likely to be encountered in practice.

A further important feature of my invention, however, consists in a specialproportioning of the constituents of such an alloy, and is not limited to an alloy of palladium and silver. It will be noted that palladium is a nonoxidizable metal having a high melting point but a low thermal-conthe other hand is a metal having a comparatively low melting point but a high When, in an alloy of palladium and silver,

proportion, because if the percentage of pale ladium be increased the thermal-conductivity of the alloy decreased, and, hence, for this reason its resistance to spark erosion is reduced, whereas if the percentage of silver is increased from said critical proportion, the melting point of the alloy is dethermal-conductivity.I

the percentage of palladium is increased, -the melting point L satisfactory with the practice without creased, and for this reason its resistance to spark erosion is reduced. I have found that such a critical proportion for a palladium-silver alloy occurs with about per cent. of silver and 40 per cent. of palladium. When an alloy of this composition is used for the terminal facings of contact devices or spark points the result will be entirely greatest density of current encountered in practice, while at the same time such an alloy is substantially mechanically inert and will not be affected by the reacting components of any atmosphere likely to be encountered in practice. It is to be understood that considerable variation from the critical proportion may obtain in material disadvantage. In fact I have found that 50 to 80 per cent. of palladium and 50 to 20 per cent. of silver form an alloy particularly satisfactory for general use.' It is clear that so far as this feature of my invention is concerned, any non-oxidizable high melting metal ,of low thermal-conductivity may be combined w1th a low melting metal of high thermal-conductivity in substantially the proper cr1t1- cal proportion so-as to producev an alloy Iha-vmg the maximum resistance to spark In the accompanying drawing, I have illustrated three curves, A, B, and C. Two of these curves, A and B, respectively show the thermal-conductivity and the melting point of alloys 'of palladium and silver of different-proportions In this diagram ,the

percentages of palladium have been platted' as abscissae, while the ordinates corresponding thereto indicate on curve B the melting points of the respective compositions and on curve A the thermal-conductivities of said compositions. It will be noted that where the percentage of silver is zero, that is `to say, where the composition is pure palladium, the melting point is a maximum. Where the percentage of silver is 100, that is to say, where the composition is pure silver, the thermal-conductivity is a maximum.

In view of my discovery that the alloy which has substantially about 60 per cent. of silver and 40 per cent. of palladium has the maximum resistance to spark erosion, the curves A and B may be so platted that they Will cross at the point corresponding to this particular alloy.' Since the resist- -ance to spark erosion falls oif when the proportions of the alloy are varied either Way from the critical proportion, a curve may be drawn to represent this resistance to spark-erosion, and it will be found that for practical purposes the first part of the curve of resistance to spark erosion may be assumed to follow the first part of the curve B, while the last part follows the last part of the curve B. Of course, the form and size of the contact point Will affect the conductivity and radiation so that for this and other reasons the curve of resistance to spark erosion may not follow exactly the curve laid down as proposed above, but for purposes of illustration of the present invention, and for practical purposes in preparing other alloys the plan suggested may be followed with satisfactory results. It is to be understood, however, that these curves are merely illustrative and are introduced principally for the purpose of giving an explanation of why a terminal comprlsing a high melting metal and a metal of high thermal conductivity will give a maximum resistance to spark erosion when combined in a certain critical proportion. Therefore, for the purpose of illustration, from the curves A and B may be deduced a curve C, indicating the resistance to spark Aerosion of an alloy of different proportions. It will be seen that this curve C reaches a maximum at a point where the alloy comprises about 40% of silver and 60% of palladium. At this critical proportion the melting point of the composition is the highest obtainable in such an alloy simultaneously with the highest thermal-conductivity of such alloy. That is to say, the alloy has the maximum resistance to spark erosion. The same principle is" applicable to other alloys compris' ing nonoxidizable high melting metals of low thermal-conductivity, and relatively low melting metals of high thermal-conductivity.

From curve C it will be noted that for a considerable distance atv each side of the maximum the .curvature is relatively flat, so that, for example, between the ordinates indicating 40 and 80% respectively of palladium, the resistance to spark erosion does not change greatly. Hence, with this alloy the proportions of palladium may be varied from 40 to 80% without material disadvantage even under conditions where the terminals are subjected to severe conditions of service.

A Vterminal facing for a contact device made of palladium-silver alloy may be somewhat softer than pure platinum, whereb considerable difficulty in fitting the surfaces to each other is avoided owing to the fact that as the composition is somewhat softer and more malleable than platinum the hammering of the contact surfaces against each other in practice will force an accurate fit of the contact surfaces, and thereby insure a satlsfactory operation of the contacts, even when not accurately fitted initially. Of course, the contacts should not be so soft as to materially flatten out after the surfaces have been brought into contact throughout.

:In practice I have found facings comprising an alloy and silver are` as satisfactory that terminal of palladium as pure plati- Licenze numI acings, While at 'the same time they are more readily Worked into shape and attached in place by soldering or the like.

`While I have particularly referred to a f terminal facing consisting of palladiuml and silver alloy, itis to be understood that my invention in its broadest aspect does not exclude such an alloy containing other constituents in addition to the palladium and silver.

What is claimed is x l. A terminal for an electric spark or contact device comprising palladium and silver.

2. A terminal for an electric spark or contact device consisting of an alloy of palladium and silver.

3. A terminal for an electric spark or contact device consisting of an alloy of palladium and silver containing from substantially 40 to 8O per cent. of palladium.A

4. A terminal for an electric spark or contact device consisting of an alloy comprising a nonoxidizable metal having a high melting point and low thermal-conductivity, and a metal havinof a low melting point and a high thermal-conductivity, the metals being combined in substantially such proportions as to give the alloy a maximum resistance to spark erosion, substantially as described.

ln testimony whereof, I have hereunto set my hand, in the presence of tWo subscribing Witnesses. Y

' PAUL R. HEYL.

Witnesses:

BENJ: B, RILEY, CHAs. D. AYLEs. 

